Simon Thomas: Could eagle ray feeding pits provide refugia from heat stress in intertidal sediment ecosystems?

<p dir="ltr">Heatwaves are increasing in frequency and intensity with climate change. Eagle rays feed on shellfish such as cockles on intertidal flats, creating pits in the sediment that hold water at low tide. These pits keep sediments cool, and could buffer ecosystems from heat stress effects, providing refugia. We tested this by simulating a heatwave in the field using heat chambers to passively heat the sediment at low tide. We compared ambient sediments and ray pits by measuring the relationship between cockles and sediment oxygen consumption and production. We found that this relationship was unaffected by heat stress in ambient sediments, but was broken in pit sediments. This is likely because pit sediments became less oxygenated under heat, causing cockles to move closer to the surface where they faced stronger heat stress. We therefore conclude that ray pits do not protect against heat stress and may even make its effects worse.</p>